A gas turbine engine such as used in aeronautics includes an upstream inlet through which air is sucked in and then compressed by being guided through the compressor stages. The compressed air is introduced into a combustion chamber, the fuel also being admitted into said combustion chamber and mixed with the air and combustion taking place in said chamber. The hot combustion gases are expanded in the different turbine stages, one of which is generally a high pressure stage directly downstream of the chamber and which receives the gases at the highest temperature compatible with the behavior of the materials. After said first expansion, the gases are expanded again by being guided through the so-called low pressure turbine stages. One turbine stage includes a wheel of distributors upstream of a turbine runner.
A distributor wheel with axial flow includes a plurality of blades arranged radially with regard to the axis of the machine connecting a ring-shaped element radially inside and a ring-shaped element radially outside; the assembly forms a ring-shaped vein facing the runner blades of a turbine wheel. The runner is itself made up of blades which extend radially from the rim of a disk or a moving drum about a rotational axis. The blades are traversed in an axial manner by the engine gases. In this way, the low pressure section of an engine generally includes several turbine stages.
The distributor wheels are segmented into a plurality of sectors which are distributed around the axis of the machine, each segment being formed by a plurality of blades between two ring sectors. Each segment is mounted inside the casing of the turbine by the ring sector radially outside. Said latter includes a retaining means upstream and a retaining means downstream. Said means, for example, are ring-shaped rails which are provided in the inside wall of the casing on which support surfaces, which are arranged on the ring sectors of the distributor segments, come to bear. The assembly is arranged so as to allow the relative expansion of the distributor with regard to the casing which is a function of the variations of the working of the machine. On account of the axial symmetry of the distributor wheels and of the tangential stresses resulting from the gaseous flow which traverses them, it is necessary to provide means for blocking the sectors from rotating.
Patent FR 2 743 603 in the name of SNECMA describes a method of assembling such distributor segments inside a casing. The distributor segments include a peripheral outside rib, at right angles to the axis of the distributor, resting by way of faces, one radially outside, the other downstream, on corresponding faces of the inside wall of the casing. Clamps, formed by the turbine ring downstream of said level, hold the segments and keep them in position against the radial movements. A protrusion on the upstream face of the rib of each segment includes a notch in which a rotation-proofing peg is housed. Said peg is made up by a head which is housed in said notch and a rod which is slid into a radial bore of the wall of the casing. In this way, said peg prevents any rotational movement of the distributor segment about the axis of said latter.
So as to protect the wall of the casing against radiant heat produced by the distributor segments, a sheet is provided interposed between the segment and the inside wall of the casing. Said heat shield sheet bears upstream against a radial surface portion which is arranged in the inside wall of the casing. The upstream edge of the shield sheet is curved radially toward the inside in order to form a pin which also bears on an upstream edge of the segment and participates in the holding of said segment against the upstream rail of the casing. Downstream the shield sheet includes an indentation with a tab in the bottom of the indentation which bears against the rotation-proofing peg of the segment. The tab is in effect wedged in a fine groove of the peg.
Said assembly provides complete satisfaction as regards holding the distributor inside the casing and protecting it thermally.
However, it has been observed that the sheet was likely to release itself from its contact with the rotation-proofing peg, the tab coming out of the bearing groove provided on the peg. By not being retained against the peg, the downstream part of the sheet, where the tab is located, is able to go and rub against the inside face of the wall of the casing, and scratch the same. It would be desirable to eliminate said risk of wear on the casing.